Method of tagging with microparticles

ABSTRACT

METHOD OF TAGGING INDIVIDUAL UNITS OF PRODUCTION OF A SUBSTANCE BY PROVIDING AN INVENTORY OF BATCHES OF MICROPARTICELS, EACH BATCH BEING UNIFORMLY CODED BY INCORPORATION IN THE MICROPARTICLES A SELECTED COMBINATION OF TAGGING ELEMENTS IN UNIFORM AMOUNTS OF AT LEAST 0.1% OF THE TOTAL WEIGHT OF THE MICROPARTICLE. UNIQUELY CODED MICROPARTICLES ARE INCORPORATED INTO EACH UNIT OF PRODUCTION OF THE SUBSTANCE WHEREBY RECOVERY OF A SINGLE MICROPARTICLE WOULD BE SUFFICIENT TO IDENTIFY THE UNIT OF PRODUCTION OF THE SUBSTANCE.

NOV. 13, 1973 R G LWESAY 3,772,200

METHOD OF TAGGING WITH MICROPARTICLES Filed April 30, 1971 H6. M F/. /0 f V wma/v5 /0 f /C/ Z zh C? /Z M75/Q @E60/Q05 Q 152/457 /5 0F 60055 Q@ United States Patent O M' 3,772,200 METHOD OF TAGGING WITH MICROPARTICLES Richard G. Livesay, White Bear Township, Ramsey County, Minn., assigner to Minnesota Mining and Manufacturing Company, St. Paul, Minn.

Filed Apr. 30, 1971, Ser. No. 139,012 Int. Cl. C09k 3/00; G21h 5 /02 U.S. Cl. 252-301.1 R 11 Claims ABSTRACT OF THE DISCLOSURE FIELD OF THE INVENTION This disclosure relates to a method of tagging a substance such as an explosive to enable subsequent indentification of the substance, its manufacturer, lot and/ or composition.

BACKGROUND OF THE INVENTION It has not previously been possible to identify a specific charge of an explosive after its detonation; obviously, a stamped lot number on the wrapper of dynamite would no longer exist after the blast. Identification of the exploded dynamite would enable authorities to place responsibility on illegal sales and/or on inadequate protection against theft. Identification of the exploded dynamite would provide authorities with knowledge of where and when the specific dynamite was stolen. Mere knowledge as to the type of explosive or that it was homemade would be valuable. Also, the psychological effect of knowing that the dynamite can now be traced, even after detonation, may be an effective deterrent to illicit use of dynamite.

Often in the case of fired ammunition the bullet is sufficiently mutilated on impact to prevent even identification of the caliber of weapon that -was used; of course, with such destruction of the bullet it has not been possible to even know the type of weapon nor to link the bullet with a suspected weapon. Law enforcement personnel could use a system of identifying the type of weapon used and the source of the ammunition when the bullet is mutilated or cant be located.

THE PRESENT INVENTION The method of the present invention enables such identification by including uniquely coded microparticles with substances to be monitored. The unique coding is providing by incorporating into individual batches of the microparticles selected combinations of the tagging elements at various concentration levels to provide an inventory of up to uniquely coded batches of microparticles Where L is the number of discrete concentration levels at which the in- 3,772,200 Patented Nov. 13, 1973 ICC dividual elements are used and N is the available number of the tagging elements. A small number of tagging elements each used at a few concentration levels provide a very large number of uniquely coded batches. For example, an inventory of microparticles might be made using as the carrier a common glass formulation of the soda lime type and adding combinations of ten selected elements at three discrete concentration levels such as 0.5%, 1% and 2% by weight. Homogeneous melts formed into microspheroids by conventional glass bead manufacturing technologies would provide, 1,048,575 different codes, each coded glass microspheroid batch being distinct from the rest.

The differently coded glass beads or microparticles can be included in each individual unit of production or lot of a substance such as dynamite and later upon recovery can readily be analyzed and correlated with previously recorded code data to identify the exact unit of production. This can be done Without necessarily (a) using a significant amount of the substance in question, (b) significantly damaging the substance, or (c) determining the composition or formulation of the substance. Actually, as with detonated explosives, the substance which contained the coded microparticles need not even be recovered. Only one coded microparticle need remain after destruction of the substance to enable complete and accurate identification.

The broadest dimensions of the individual microparticles may be as small as one micron, but should be no larger than 250 microns so that only a small weight percent of microparticles need be incorporated into a given substance to provide a sufficient number to guarantee recovery of at least one microparticle. It is believed that microparticles in excess of 20 microns minimize possible health hazards and facilitate the separation and identification of the microparticles from the extraneous matter. Micropheroids having diameters ranging between 20 to 100 microns having been used effectively and eiciently.

The outward shape of the microparticle may be determined by a particular strength requirement and/or t0 provide a shape that is easily differentiated from extraneous matter under a microscope. Glass microspheroids used to tag dynamite have withstood its explosion and were readily distinguishable by their shape from the debris. While microspheroids are preferred, the microparticles may be flakes, fibers, columns or rods, etc., especially where the substance to be tagged comprises microspheroids.

The density of the microparticle may be adjusted to aid in separating the microparticle from the extraneous material. For example, microparticles having a density of about 4 ,gm/cm.3 having been readily separated from dirt and common debris which generally has much lower density, and for this reason a density of at least 3 is particularly advantageous. To permit magnetic separation of the microparticle from the extraneous material, the microparticles may include magnetic fragments.

In order to be impervious to or unaffected by the substance carrying the microparticle or by any environment to which it will be exposed, the microparticle should comprise glass (vitreous) or ceramic (crystalline) or other refractory material, or possibly a metallic material.

The tagging elements may be selected from any of the presently available chemical elements. Hhowever, the elements having high natural radioactivity would be generally excluded for health and ecology reasons. The following elements are preferred:

*Aluminum *Niobium (columbium) *Antirnony Osmium *Arsensic Palladium *Barium Platinum *Bismuth *Potassium *Cadmium *Praseodymium *Calcium Rhenium *Cerium Rhodium Cesium Rubidium *Chromium uthenium *Cobalt amarium *Copper Scandium Dysprosium Selenium Erbium *Silicon Europium *Silver Gadolinium *odium *Gallium trontium *Germanium *Talrtal'um Gold Te urium Hafnium Terbium Holrnium Thallium *Iridium *Thor'ium Iridium 'Ihulium *Iron *Tin *Lanthanum *Titanium *Lead *Tungsten (Wolfram) *Lithium *Uranium Lutetium *Vanadium *Magnesium Ytteibium *Manganese Y'ttrium *Molybdenum *Zinc *Neodymium *Zirconium *Nickel The tagging elements may be selected to avoid those elements used in the carrier itself. On the other hand, the elements inthe carrier may be included in the code to permit occasional shifts in codes by changing the carrier material. For example, all microspheroids applied to each manufacturer of dynamite may have a unique carrier simply to dilerentiate from other manufacturers. Those common impurities present in relatively high concentrations in refractory carrier materials should be avoided as tagging elements. However, parts per million contaminants, within the carrier or tagging raw material, will not normally interfere. The starred elements in the above table are believed to have particular advantage because of economic considerations.

The tagging elements may exist in the microparticle as a free element, an oxide or other compound thereof. In the ultimate analysis, only the element itself is detected, and its existence in the microparticle as a free element, its oxide or other compound thereof is not differentiated.

As noted above, the microparticles may be coded both by selected combinations of the tagging elements and by the levels at which the tagging elements are used. Each tagging element should be incorporated in an amount of at least 0.1 percent of the total weight to provide an efficient analytical operation with an electron microprobe analyzer, the present instrument of choice. Because of practical limits with the present analytical instruments, it is believed that the levels of one element should vary from one batch of microparticles to the next by a factor of at least 1.5, a factor of 2 being preferred. For convenience of analysis, the lowest level of each element may be the same, for example, 1%. However, some elements lend themselves for use at greater numbers of levels than do others, in which case the number of unique codes becomes:

wherein La, Lb, and Lc are the number of levels for elements a, b and c, respectively, and so on for the N elements selected for a particular inventory.

When the microparticles from one batch are incorporated into an individual unit of production of a substance, it will be necessary to retain recorded data of the code and the unit of production (e.g., date, manufacturing plant, etc.) for subsequent correlation. The records may also include specimens from each batch to provide rigid conrmatory analysis of the recovered microparticle should the need arise.

The microparticles could have utility without the same being included within a specific subject but could be merely associated with a substance or placed in anarea to be subsequently acquired by a substance.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1A is a diagrammatic illustration of a microspheroid;

FIG. 1B is a cross-sectional view of a microspheroid having tagging elements interspersed homogeneously throughout a glass carrier; and

FIG. 2 is a diagrammatic use sequence illustrating a system of providing coded microparticles within dynamite to enable tracing of the explosive to its manufacturer after detonation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The sphere-like microparticle 10 (microspheroid) illustrated in FIGS. 1A and 1B includes tagging elements homogeneously interspersed throughout a refractory carrier material. FIG. 2 of the drawing is discussed below in Example VI.

The following Examples I-V illustrate live specific microparticle compositions. All percentages stated herein are by weight.

Example I This composition utilized finely powdered metal oxides, M002, La203, Ce02 and W03, all of standard laboratory stock chemicals. Although these were of high purity, any degree of purity above is acceptable. 'Ihese oxides were weighed to provide metal oxide levels of 18.0%, 31.6%, 33.3% and 17.1% respectively, giving integer ratios of l:2:2:1 for the individual metals themselves. The mixed metal oxides were intimately mixed with BaO-TiOz glass beads to the extent of 4 g. mixed metal oxides to 76 g. of glass beads. The mixture, in a crucible, was tired at about 1400 C. to a homogeneous (by thermal convection) melt in a gas fired furnace. Ihe resulting melt was jet formed (a method conventional to the glass bead industry) to sphere-like microparticles, cooled, and screened to to 325 mesh fraction (U.S. Standard Sieve) having a thickness range of to 44 microns. This produced clear, buff colored microspheroids.

Example II A second composition was prepared using the metals Zn, Sr, Cd and Nd in an integer ratio of 4:2:2: 1, respectively, as their oxides except for strontium which was added as its carbonate. The metal oxide-carbonate mixture was weighed out to contain 44.2%, 28.6%, 19.3% and 9.9% of the respective compounds, and the well mixed materials were added to BaO-TiO2 glass beads. From this,

' sphere-like microparticles were made as described in Example I. This produced clear, off-white (in bulk) microspheroids of 37 to 149 micron range (400 to 100 mesh). The loss of CO2 from the carbonate in the melt step was not detrimental.

Example III A third composition was prepared using MnO2, NiOY and SnO in weighed proportions of 26.5%, 42.7% and 19.0%,

C0203, 1 1.8 respectively, to give a metals integer ratio of 2:1:4:2. The metal oxide mixture was intimately mixed with BaO-TiOz glass beads and sphere-like microparticles were made therefrom as described in Example I. This composition produced a clear black colored (in bulk) microspheroid product.

All of the microparticles of Examples I, II, and III had densities greater than 3.3 g./cc., a useful property for facile separation from other substances.

Example IV A fourth composition was a sol-gel preparation of microparticles. A clear, colorless solution was prepared by dissolving with agitation in 110 g. of Iwater 42.70 g. aluminum acetate [Niaproof (TM)] containing the equivalent of 19.0 g. 3Al2O3-B2O3. With continued agitation was added 1.44 g. MnCl24H2O dissolved in 10.0 g. water (0.40 g. Mn), 0.474 g. Cd(CH3COO)2-2H2O dissolved in 10,0 g. Water (0.20 g. Cd), and 1.064 g. CeCl37H2O dissolved in 10.0 g. water (0.40 g. Ce) to give a clear, colorless solution containing:

2% Mn, Cd, Ce and 3A1ZO3'B203 Eighty grams of tbe solution Was slowly poured into 3.5 liters of Z-ethylhexanol at room temperature While being agitated at about 800 r.p.m. with an air motor driven paddle type mixer in a 4-liter beaker. Agitation was continued for an additional 20 minutes to extract water from the microdroplets of solution in the alcohol. The wet alcohol was removed by filtration through l#54 Whatman lter paper to recover transparent, colorless sphere-like particles of 20 to 100 microns size range. 'Ihe particles were dried in an oven at 90-l00 C. for 1% hours to remove residual alcohol and then placed in a porcelain crucible in an electric furnace at room temperature. 'Ihe furnace temperature was raised to 600 C. over a 11/2 hour period, then raised to 850 C. and held at this temperature for an additional 1 hour. The yield was 7.3 g. of light brown, transparent microspheroids.

Example V A higher density microparticle than described in Example IV was prepared by using a carrier consisting of ZrO2:SiO-2 (1:1) in the following manner: To 58.75 g. zirconium acetate solution (equivalent to 12.9 g. Zr02) was added 0.72 g. MnCl2-4H2O (0.2 g. Mn), 0.95 g. Cd(CII3COO)2-2H2O (0.4 g. Cd), and 0.53 g. CeC13-7H2O (0.2 g. Ce).

The salts dissolved readily to form a clear, colorless solution. To this solution was added with agitation an aqueous dispersion having a pH of about 1 prepared from 21.0 g. colloidal silica (30% SiO2) plus 10 drops of concentrated hydrochloric acid. Although the resulting dispersion was slightly cloudy, it Was colorless and there was no trace of particulate matter apparent. This dispersion was gravity fed through a syringe into 3.5 liters 2-ethylhexanol at room temperature while being agitated as in Example IV, but at about SOO-1000 r.p.m. The addition required about one minute and stirring was continued for 20 minutes to remove water from the microdroplets in the alcohol. The wet alcohol was removed by filtration through #54 Whatman iilter paper to recover clear, colorless microspheroids of 2O to 120 microns size range. These were dried at 90- 100 C. for one hour and then placed in a porcelain crucible in an electric furnace and raised to SOO-820 C. over a 3-hour period and cooled. About 20 g. of lavenderbrown, transparent microspheroids were obtained.

Other coded microspheroids were made with 3, 4 and 5 different tagging elements at various concentration levels and with various carriers such as titania, alumina and alumina-borosilicate using4 the techniques of Examples IV and V.

The coded microparticles, such a's those from Examples I-V, are produced and maintained in individual batches wherein each and all of the microparticles within one batch will have an identical code. Microparticles from any one batch may then be added to a lot or unit of production of a substance for coding the same. For example, the microparticles may be added: to paper for use as money, securities, bonds, documents, labels, etc.; to adhesives, coatings, sealants, etc.; to plastics, resins, foams, etc.; to pharmaceutical items such as drugs, narcotics, medicinals, etc.; to explosives such as gun powder, dynamite and other propellants for munitions; to surface coating substances such as paints, lacquers, enamels pigments, waxes, etc.; and other manufactured goods.

Paint-like coating substances containing coded microparticles may identify objects such as automobiles. A given code applied to a single automobile or to a series of automobiles would provide identification that would be nearly impossible for a thief to locate rand remove. Identifying paint fragments containing the microparticles might be found on a hit-an-run victim or, in the case of tagged tools, might help convict a burglar.

The following Examples VI-VIII illustrate three instances wherein coded microparticles such as those produced in accordance with Examples I-V have been incorporated, recovered and used to identify a specific substance.

Example VI To 'assist in understanding this example, reference is additionally made to FIG. 2 of the drawing.

Microparticles 10 of Example I with their identical and unique code noted (in the records 11) were added to dynamite 12 at a weight ratio of 1 part identifier to 1000 parts dynamite. After detonation of the dynamite (1 pound charge), approximately 1.5 kg. of debris 14 was collected from the blast crater 15. The collected debris was then washed with tap water to remove microparticles clinging to the larger objects, after which debris objects in excess of approximately 1A inch in diameter were manually discarded. The remaining blast debris was then thoroughly dried. A representative sample (approximately 1/5 to 1A of the Whole collected debris) was screened through a 60 mesh sieve onto glazed paper to eliminate relatively coarse debris which Was discarded. The lines were rescreened through a mesh sieve onto glazed paper. Approximately 10 grams of fines were added to a beaker and wetted with acetone. The wetted fines were repeatedly washed with tap water and then with acetone and then dried and transferred to a separation tube, made from a drawn-down 15 rnl. centrifuge tube containing 8 to 10 ml. of diiodomethane (CH2I2) having a density of 3.3 gm./cm.3. 'Ihe slurry of solvent and lines was carefully agitated above the constriction of the separation tube with a tapered spatula for approximately 10 minutes to allow dense particles (those with densities greater than 3.3 gm./cm.3) to settle through the gangue to the bottom of the narrow section. The tube was immersed in an ice bath to freeze the solvent (M.P. 5-7 C.). The separation tube was broken at the constriction, and the smaller portion of the tube with the denser lines therein was placed within a small beaker. Approximately half of the melted solvent was removed with a serological pipette, and a permanent magnet was then drawn up the side of the small tube to remove any magnetic particles present. The remaining dense fines and residual solvent were transferred to a 5 cm. Petri dish, and the CH2I2 was removed by repeated washings and decantations with acetone. The dense lines were then carefully dried and examined under a stereo microscope, and a number of the microspheroids 10 were apparent. One of these was removed with a sharp dissecting needle and placed on a glass disc mount for analysis using a Model 400 Electron Microprobe Analyzer (diagrammatically illustrated at 16 in FIG. 2) made by the Materials Analysis Company. The qualitative and quantitative analysis 18 matched (illustrated at 20) the records 11 for the dynamite that had been detonated.

7 Example VII To 30 g. of an alkyd automobile enamel (Ditzco Enamel DOE-8238 manufactured by Ditzler Automotive Finishes, a subsidiary of Pittsburgh Plate Glass Company) was added 0.03 g. sol-gel microspheroids (produced similarly to the microspheroids of Examples IV and V) with Co, Ni and Sr as coding elements in integer ratio of 412:1. The coded paint was thoroughly mixed by hand shaking in a covered glass jar of 120 cm.3 (4 oz.) capacity for several minutes. This gave a 1:540 identifier to enamel ratio based upon 54% solids content.

Three of four previously cleaned and dried plates of 5 cm. x 10 cm. x .56 mm. (2" x 4" x .022) galvanized sheet metal were divided transversely into two equal areas with .6 cm. (MW) strips of masking tape. One-half of each of the three divided plates was brush painted with coded enamel and the other half with the original uncoded enamel. 'Ihe fourth plate was completely painted with the coded enamel and cemented firmly near the end of a piece of wood approximately 36 cm. x 5 cm. x 1.3 cm. (14l x 2" x 1/2) and all of the painted plates were air dried at ambient temperature and relative humidity for one hour, then further dried for one hour under a 300 watt infrared heat lamp at 76 cm. (30) distance.

'Visual inspection of the painted specimens revealed no differences in appearance to the unaided eye. Under 60X magnification, probing with a dissecting needle readily revealed microspheroids within the coded enamel. The specimen attached to the wooden handle was beaten severely against a mounted metal knob as a crude simulation of an automobile impact. Visual examination of the knob revealed transfer of enamel fragments. Under the microscope, microspheroids were observed in the transferred fragments.

A separated microspheroid was analyzed according to method described in Example VI and shown to be the CozNizSr (422:1) coded microspheroid incorporated originally into the enamel.

'Example VIII Thirty-two rounds of 9 mm. antebellum Walther P-3-8 pistol ammunition were unloaded and the 11.2 g. (175.2 grains) of the collected powder was mixed with 12.5 mg. of microspheroids of Example III. This gave a powder to identifier ratio of 910: 1. The intimately mixed powdermicrospheroid combination was then reloaded into the previously emptied rounds for use in firing tests.

A cardboard cylinder was firmly packed with sawdust which was retained with a cardboard disc. To this cardboard disc was secured a piece of beef and draped with a clear piece of linen cloth to serve as a crude representation of a clothed iiesh target. A rst round containing the mixed powder-microspheroid combination was fired into the horizontally suspended target from approximately 6 rn. (20 feet). Before firing the second round, the beef, cloth and cardboard disc were all replaced and this sequence was repeated for a total of five rounds. The punctured target cloths, meat pieces and cardboard discs were individually packaged in polystyrene bags and labelled. The same was done for cleaning swatches used to clean the barrel after the tests, one package of swatches bearing cleaning solvent and oil and a second package item and analyzed as described in Example VI to confirm the original code.

In the case where quantities of microspheroid coded dynamite may be acquired or stolen from more than one source, combined and used in a criminal blast, it has been shown that microspheroids recovered from the blast debris did in fact represent the several sources. This was demonstrated in a test blast using three differently coded identifiers all at 1:1000 identifier to dynamite ratio, and the analysis correctly revealed that the three coded dynamites had been used.

It is appreciated that analytical techniques and instrumentation other than the electron microprobe analysis cited in Example VI may be utilized within the teachings of this invention. 'For example, neutron activation analysis, atomic absorption spectroscopy, emission spectroscopy, energy-dispersive X-ray analysis, electron paramagnetic resonance spectrometry and spark-source mass spectrometry could be employed to analyze isolated microparticles.

It is anticipated that this invention might have utility in tagging drugs in which case it may be required, for government approval, to use a biodegradable carrier material such as a material of polymeric nature.

What is claimed is:

1. A method of tagging individual units of production of a substance comprising the steps of: (l) providing microparticles of a refractory carrier material of characteristic geometric shape and size, the broadest dimensions of which are not less than one nor more than 250 microns, containing tagging elements in amounts of at least 0.1 percent of the total weight, which microparticles have a density greater than 3.3 g./cc. and survive ashing at 400-500 C.; (2) providing an inventory of batches of microparticles, each batch being uniformly coded by ncorporation in the microparticles of a selected combination of the tagging elements, which inventory includes up t0 uniquely coded batches of microparticles where L is the number of discrete concentration levels at which the individual elements lare used and N is the number of available tagging elements, and the microparticles of at least some of the batches contain at least three tagging elements, (3) maintaining a record of the particular elements and their levels employed in each batch of microparticles, and (4) incorporating microparticles from any one batch with only one unit of production of the substance, recovery of a single microparticle being suiiicient to identify the unit of production Iof the substance.

2. A method of tagging individual units of production of a substance according to claim 1 wherein L equals one and qualitative analysis of a microparticle will identify the unit of production of the substance.

3. A method of tagging individual units of production of a substance according to claim 1 wherein L is greater than one and both qualitative and quantitative analysis of a microparticle will identify the unit of production of the substance.

4. A method of tagging individual units of production of a substance according to claim 3 wherein the discrete level of at least one element will vary from one batch of microparticles to another by a factor of at least 1.5.

5. A method as defined in claim 4 wherein N is at least 10 and L is at least 3.

6. A method of tagging individual units of production of a substance according to claim 1 wherein said carrier material is vitreous in nature.

7. A method of tagging individual units of production of a substance according to claim 1 wherein said carrier material is crystalline in nature.

8. A method of tagging individual units of production of a substance according to claim 1 wherein each microparticle is spheroidal.

9. A method as dened in claim 8 wherein the spheroidal microparticles are between 20 and 100 microns in diameter.

10. A method of tagging individual units of production of a substance according to claim 1 wherein the microparticles from a single batch are incorporated into a paintlike surface coating.

11. A method of tagging individual units of production of a substance according to claim 1 wherein the available tagging elements are:

Aluminum Neodymium Antimony Nickel Arsenic Niobium (columbium) Barium Potassium Bismuth Praseodymium Cadmium Selenium Calcium Silicon Cerium Silver Chromium Sodium Cobalt Strontium Copper Tantalum Gallium Thallium Germanium Thorium Indium Tin Iron Titanium Lanthanum Tungsten (Wolfram) Lead Uranium Lithium Vanadium Magnesium Zinc Manganese Zirconium Molybdenum April 1969.

References Cited UNITED STATES PATENTS OTHER REFERENCES Tracy, Coding Documents by Trace Element Inclusion (IBM Technical Disclosure Bulletin, vol. 11, No. 11)

Horowitz et al., Proceedings of the Joint Conference on Prevention and Control of Oil Spills, pp. 283-296 (1969), American Petroleum Institute, New York.

CARL D. QUARFORTH, Primary Examiner E. A. MILLER, Assistant Examiner U.S. Cl. X.R.

117-161 K; 149-2; Z50-106 T 

